The long range purpose of the present project is to investigate the role of retroviruses in the etiology of reticulum cell as well as other lymphoid cell neoplasia, and to study the functional markers and surface antigens of tumor cells. The topics of current interest are: 1) Isolation and characterization of ecotropic and xenotropic retroviruses from SJL/J strain of mouse which exhibit a high incidence of spontaneous reticulum cell neoplasm (RCN); 2) Transplantable RCN exhibiting a killer activity against some other tumors; 3) Distinction between viral structural proteins (VSP) and tumor specific transplantation antigens (TSTA); and 4) Virological and immunological aspects of a nonproducer hemangioma originally induced by Moloney-MSV. BIBLIOGRAPHIC REFERENCES: Chang, K. S.S.: Susceptibility of xenoderma pigmentosum cells to transformation by murine and feline sarcoma viruses. Cancer Res., 36: 3294-3299, 1976. Liu, W.-T., Rogers, M.J., Law, L. W. and Chang, K. S.S.: Properties of RBL-5 leukemia cells cultivated in vitro. J. Nat. Cancer Inst., 58: 1661-1664, 1977.